Why wont my 'background' render?
Empties have no geometry

You are using an Empty object to display the image (you can that from the icon in the outliner), but as stated by the manual:


  The “Empty” is a null object. It contains no real Geometry, [...]


This means that the object has no faces, no materials, so the engine has nothing to render. What you see in the viewport is just a "gizmo", useful to work with but has no influence on the rendered image.

The Image-Empties can be useful to quickly put some movable references in the scene. If you want to render the image, I would suggest to use the Images as plane add-on, that starting from an image create a true object in the scene.